Engineering Design Notes III Conceptual Design. EE 498/499 Capstone Design Classes Klipsch School of Electrical & Computer Engineering

Transcription

1 Engineering Design Notes III Conceptual Design EE 498/499 Capstone Design Classes Klipsch School of Electrical & Computer Engineering

2 Topics Overview Definitions Conceptual Design Steps Activity Analysis Concept Generation Analysis and Feasibility Evaluation Methods Documentation Spring 2007 Design Notes III - Conceptual Design 2

3 Overview The Conceptual Design is the first part of the design process after the specifications have been determined. This is to act as the intellectual exercise to generate ways accomplishing the actual design. This step is successful if we have at least one feasible alternative to work with when we are done. Redesign iteration Specification Generate Alternatives Analyze Alternatives Evaluate Alternatives Establish functional requirements Determine design constraints Determine acceptance criteria Create alternative solutions to realize Specifications Feasible Alternatives How well do the alternative designs meet the Specifications Perform numeric comparison of the alternatives and the quality of their meeting Specifications Fabrication specification for the best alternative Design Process Version I Spring 2007 Design Notes III - Conceptual Design 3

4 Definitions What is the Conceptual Design process? It is the generation of design alternatives or Design Concepts and the supporting analysis to determine the feasibility of each alternative. What is a Design Concept? It is a design alternative that includes at least one physical principle and one abstract embodiment. Spring 2007 Design Notes III - Conceptual Design 4

5 Definitions What is a physical principle? This is a natural law or effect that produces a useable method of modifying a signal or device to produce a functional output. For example, the photoelectric effect is a physical principle that produces a current in proportion to the intensity of the incident light. An abstract embodiment is a diagram that shows the relative relationship between the actors in the design. It need not be to scale. Spring 2007 Design Notes III - Conceptual Design 5

6 Definitions Examples Design Element Physical Principle Embodiment Method Energy Generation Photoelectric Effect Solar Cells Nuclear Power Combustion Reactor Furnace Data Communications RF Optical Radio/modem Laser/detector Wire Wiring harness Energy Storage Chemical Storage Battery Spring 2007 Design Notes III - Conceptual Design 6

7 Definitions The Conceptual Design Diagram is A diagram with the Design Concept, Including the physical principles being used, and The abstract embodiment. This is basically a block diagram or extended sketch with the necessary aspect labeled. Note: systems usually need to have individual Conceptual Design Diagrams for the component subsystems rather than all-in-one diagrams. Spring 2007 Design Notes III - Conceptual Design 7

8 Definitions Example: Develop a Conceptual Design Diagram for a communications system composed of a modem, RF transmission unit, and antenna. Note, actual components not specified at this level. Potential Physical Principles that can be considered: RF, Optical, or Wire harness communications. Here, we consider the Conceptual Design Diagram for the RF option. The RF embodiment is based on a RF unit and a modem. The following diagram shows the Concept. Spring 2007 Design Notes III - Conceptual Design 8

9 Definitions Communications Conceptual Design Diagram Spring 2007 Design Notes III - Conceptual Design 9

10 Conceptual Design Steps The proper Conceptual Design Process has the following stages: Activity Analysis: how will the design be used in various stages such as normal use, battery recharging, disposal, start-up and shutdown, etc., as appropriate for the needs. Generate Alternative Concepts: the design team uses various strategies to generate Concepts that should meet the design requirements. Spring 2007 Design Notes III - Conceptual Design 10

11 Conceptual Design Steps Conceptual Design Process (cont.) Analyze: use engineering analysis, simulation, bench testing, etc. to verify that the design concept does work to meet the specifications. Feasibility Test: does the design analysis indicate that the design concept will meet the specifications and actually can per executed. Evaluate: determine which one or set of the feasible design concepts left are best (at least at the level we can tell at this time). Spring 2007 Design Notes III - Conceptual Design 11

12 Activity Analysis The Activity Analysis stage really is an exercise to determine how the design meeting the specifications is to be used in real life. This includes user activities and understanding the inputs and outputs (signals, power, etc.). To do this activity, you will need to perform a functional decomposition and an I/O analysis. Spring 2007 Design Notes III - Conceptual Design 12

13 Activity Analysis The functional decomposition takes the design functional requirements and refines them respective subfunctions and sub-subfunctions. The functions are not broken down by expected embodiments but by similar functions. Spring 2007 Design Notes III - Conceptual Design 13

14 Activity Analysis The I/O analysis looks at the control, data, and power signals coming into and out of a function. This will become a basis for the design s Interface Control Document that specifies and documents all interface details. Spring 2007 Design Notes III - Conceptual Design 14

15 Activity Analysis Comms Example Functional Decomposition Antenna Transmit Frequency Receive Frequency RF unit Transmit Electronics Receive Electronics Computer Control Set Frequencies Set Power Modem unit Waveform Processing Computer Control Set Baud rate Set comms parameters Buffer data Comms Example I/O Analysis Antenna RF signal in RF signal out RF Unit Computer interface RF signal in RF signal out Signal from modem in Signal to modem out Power Modem unit Signal from RF in Signal to RF out Computer interface Power Spring 2007 Design Notes III - Conceptual Design 15

16 Activity Analysis Activity Analysis results: An assessment of which functions can be combined A check-off to ensure that all required functions are addressed An understanding of the required interfaces A possibility that the design requirements may need to be reviewed and iterated upon to update them. Spring 2007 Design Notes III - Conceptual Design 16

17 Concept Generation The design team uses various strategies to generate Concepts that should meet the design requirements. This is also sometimes called synthesis. Use brainstorming, past experience, similar designs, Google searches, WAG s, sleeping on it, etc. This process may take some time! Spring 2007 Design Notes III - Conceptual Design 17

18 Analysis and Feasibility Analyze: use engineering analysis, simulation, bench testing, etc. to verify that the design concept does work to meet the specifications. Feasibility Test: does the design analysis indicate that the design concept will meet the specifications and actually can per executed. From the analysis and testing, we should also eliminate those designs that can t be built, would cost too much, etc. Spring 2007 Design Notes III - Conceptual Design 18

19 Evaluation Methods Once the design concepts are generated and evaluated for feasibility, the surviving design concepts need to be evaluated to determine which one is best. How does one define best? One common method is to use the criteria for the design and weight the relative importance to determine best. Note: the designers must be careful not to rig the weighting to make a favorite come out best. Spring 2007 Design Notes III - Conceptual Design 19

20 Evaluation Methods Weighted Evaluation Method: Select the evaluation criteria and place in column 1 of a matrix. Importance weights are assigned to each criterion and placed in column 2 of the matrix. The concepts to be evaluated are placed in subsequent columns of the matrix. Each concept is rates against the criteria and a score of 0 to 4 is given. A 0 implies unsatisfactory performance while a 4 is implies very good performance. Each score is multiplied by the weighting factor and the scores are summed. Highest weighted score wins. Spring 2007 Design Notes III - Conceptual Design 20

21 Evaluation Methods External COTS Modem Concept Alternatives DSP Modem Internal Modem Criteria Importance Weight (%) Rating Weighted Rating Rating Weighted Rating Rating Weighted Rating Operating current Physical Size Mass Cost Buffer Capacity Example evaluation matrix. Notice, functional requirements are not included because it is assumed that all design concepts meet the testable requirements. This is for the intangibles or more subjective criteria. Testable requirements with varying degrees of performance can also be included. Spring 2007 Design Notes III - Conceptual Design 21

22 Documentation At the end of the Conceptual Design stage, the following documents should be part of the design documentation, at a minimum: Operations Concept document Conceptual Design Diagram Function Decomposition I/O Analysis Design Analysis showing that Conceptual Design meets requirements Design Evaluation matrix Spring 2007 Design Notes III - Conceptual Design 22

23 Documentation Additional documents that can be started at this stage include: Budgets: mass, size, link analysis, power, etc. Start considering how the various components will be integrated and tested. Integration and test plans can be started. Note, in some cases, these will be no more than outlines with placeholder sections to be developed further. Spring 2007 Design Notes III - Conceptual Design 23